Coherent Anti-Stokes Raman Scattering (CARS) will be used to monitor the structure of flavin, in situ, in relation to its role in biological electron transport processes, including the microsomal hydroxylation system responsible for drug clearance and carcinogen activation. Flavoproteins chosen for study include flavodoxin, d-amino acid oxidase, and NADPH cytochrome P450 reductase, the enzyme primarily responsible for sequential electron transfer in the microsomal xenobiotic hydroxylation system.